1. Field of the Invention
The present invention relates to a liquid crystal display.
2. Description of the Related Art
A low contrast ratio is one problem of an in-plane switching (IPS) LCD that uses the nematic phase. The reasons for this are considered to be associated with an increase in the transmittance during black presentation. This is because nematic liquid crystals having a uniaxial anisotropy fluctuate with heat, thus producing regions in which the alignment directions thereof are different. Thus, the refractive indices change from place to place and from time to time, and light scattering occurs. Therefore, the use of optically isotropic liquid crystals which are liquid crystal phase without any anisotropy is being considered.
As a liquid crystal display device which does not require a surface alignment treatment nor cause alight leakage during black presentation (instead providing a dark visual field) and remarkably improves the response speed during video presentation, a liquid crystal display device which is formed from polymer-stabilized blue-phase liquid crystals interposed between a pair of transparent substrates is known. The liquid crystal display device that uses the polymer-stabilized blue-phase liquid crystals exhibits a large birefringence change in response to application of an in-plane electric field to a cell substrate. The polymer-stabilized blue-phase liquid crystals are made up of low-molecular liquid crystals capable of exhibiting a blue phase between the cholesteric phase and the isotropic phase and a polymer network formed in the low-molecular liquid crystals. In addition, a liquid crystal display device in which the kinds and amounts of chiral dopants added to liquid crystals are optimized so as to prevent the occurrence of the light leakage during black presentation (instead providing a dark visual field) is proposed in WO2005/090520.
In addition, JP-A-2008-266633 discloses a polymer/liquid crystal composite material, which is capable of exhibiting high durability and reliability in regards to the light leakage caused by repeated driving of a liquid crystal display device or the like having an optical isotropy when no electric field is applied and achieving a low driving voltage, and which has excellent phase stability with a low polymer content, and a polymer-stabilized blue-phase liquid crystal display device using such a material. The polymer/liquid crystal composite material is obtained by dispersing a polymer unit of a specific polyfunctional compound and a polymer unit of a monofunctional compound in a liquid crystal material having no polymerizable group and polymerizing the dispersion in an optically isotropic phase state. In the obtained polymer/liquid crystal composite material, at least a part of one of the polymer units originates from a methacrylate skeleton-containing compound, at least a part of the other polymer unit originates from a acrylate skeleton-containing compound, and the content of the polymer unit originating from the methacrylate skeleton-containing compound is 1 to 99 mass % with regards to the total weight of a copolymer of the polymer units. The polymer/liquid crystal composite material consists of 1 to 40 mass % of the copolymer and 99 to 60 mass % of the liquid crystal material exhibiting a chiral nematic phase or a blue phase at room temperature.